The camera page has more details about the controls. The additional parameters are shown below.
While this method creates a very nice 3D effect for objects around the viewer, some nasty artifacts will appear at the top and bottom poles. This is because the camera offset makes it impossible for the rays to reach the top and bottom positions as you can see here:
Here you can see an example of how poles look like in this case:
We can fix these artifacts by smoothing the camera displacement when rays point upwards or downwards. This solution will remove the stereoscopic effect in the poles, but in practice, it is not very noticeable. In this case, the camera rays will look like this:
The pole merging will generate a result like this:
Different settings are provided to control this pole merging so it can be adjusted depending on the scene. First, top and bottom poles parameters are independent as they could have different requisites in your scene. For example, the pole merging at the floor might need to be very smooth if it has a lot of detail, but top merging can be more aggressive if it has a flat color, giving the upper hemisphere a more relevant stereoscopic effect. An aggressive merging at the top will look like this:
Pole Merging Workflow
To maximize the stereoscopic effect in the scene while avoiding poles artifacts, the top and bottom poles can be adjusted independently to better suit the specifics of a scene.
The artifacts at the poles can be of two different kinds:
The single image you see from an eye has some deformations at the poles. Perpendicular lines do not meet at 90 degrees. These artifacts tend to appear as you increase the Merge Angle. Some examples:
When you take a look at a single eye image, you might notice a different distortion, but when you see both right and left images, you will notice a circular wave on the pole. Here is an example: